Cleveland Browns’ Johnny Manziel (2) on the bench during the second half of an NFL football game against the Carolina Panthers in Charlotte, N.C., Sunday, Dec. 21, 2014. The Panthers won 17-13. (AP Photo/Bob Leverone) more >

BEREA, Ohio — Humbled by his rough rookie season, Johnny Manziel promised to be a more committed quarterback.

The NFL knocked some of the air out of Johnny Football.

“I’m not the guy that I’ve always been,” he said. “I’m not the Johnny Manziel that came in here a year ago. It’s been a year of growing up for me.”

Manziel, who won’t play in the finale at Baltimore because of an unspecified hamstring injury, said Tuesday that he may have misjudged how difficult it would be to transition from college to the pros.

But after 13 games as a backup and two starts in which he seemed overwhelmed and unprepared, Manziel realize he must change.

“This is a job for me now and I have to take it a lot more seriously than maybe I did at first,” he said.

Manziel wouldn’t acknowledge that maybe his well-chronicled offseason lifestyle, which included trips to Las Vegas, the photo of him drinking champagne while floating in a pool on an inflatable swan, or hanging out with pop star Justin Bieber, may have affected his readiness to play.

However, he does realize it shaped his perception outside the Browns’ headquarters.

“I’m sure for me, I haven’t painted the greatest picture of me of being in here and staying on top of myself,” he said. “I’m sure with the stuff I’ve done off the field it’s negatively affected that.

“But I know, and what matters to me most, the guys in this locker room see I’m in here working and these coaches know this is my life and this is my job and I’m 100 percent committed to that.”

Manziel said when he entered the league he was “a kid who still had a college mindset a little bit.”

He insists those days are over.

“That has absolutely faded from my mind and now I think this year has really helped mold me into a pro and figure out how this league works and what it takes,” he said. “So there was a lot of learning to do throughout this year and I think it’s for the better for me as a person and as a player.”

In his brief playing time, the former Heisman Trophy winner did little to convince the Browns, who traded up to select him with the No. 22 overall pick, that he should be their quarterback of the future.

Manziel led the Browns on just two scoring drives in nearly seven quarters of action, but he didn’t display any of the improvisational magic that made him a star at Texas A&M.

He knows it didn’t look good, but he doesn’t think it would be fair for the Browns to assess his potential with just a minimal amount of time on the field.

“This league is a process and it takes a lot of time,” Manziel said. “Nobody comes in this league right away — and I mean nobody comes in this league right away and just absolutely kills it. That’s just not the way it works.”

The Browns have some big decisions to make in the offseason, starting at quarterback. Manziel, the team’s 21st starter since 1999, hopes he’s part of their long-term plans.

“Depending on how things play out, I want to be the guy here,” he said. “I think it’s my job and I want to take it that way and take it seriously every single day.”

There’s one thing Manziel won’t change. He has no intention of scrapping his finger-rubbing “money” gesture, which opponents delighted in doing when he was sacked.

“It’s been a part of who I was in college and I see me growing up and maturing moving forward, and that’s something that’s just fun to do,” he said. “When I’m out on the field, I’m not thinking about that. I’m not thinking about being an adult. I’m thinking about football’s a kid’s game that you’ve played since you were in the backyard when you were 8 years old.